re: "undocumented". I bought whatever big oreilly book there was on it - "building XUL apps" or similar (https://www.oreilly.com/library/view/creating-applications-w...) it was impossible to follow. Granted, some new-to-me concepts and such in there, but after having respected colleagues try to work through the book with me, and they also gave up, I had to conclude this was not something worth pursuing. I mean no explicit disrespect to the authors; any book is a big effort, and the publisher sometimes overrides decisions or releases something too early. In any event, I vacillate between 'what a big missed opportunity' and 'we all dodged a massive bullet there' - I still can't decide which.